Organic Chem II, Exam 2 notes

Page 1: Complex Splitting and Coupling Constants

• Complex splitting observed in NMR spectra, specifically involving proton signals.

• Coupling constant (J): Indicates interaction between splits. Notably:

  • J values for different configurations:

    • J(trans) = 11-18 Hz

    • J(cis) = 5-10 Hz

    • J(geminal) = 0-3 Hz

• Splitting of protons:

  • Hb is split by both Ha and Hc resulting in a doublet.

  • Count total protons for splitting: 5 protons + 1 = b.

• Example of C=C splitting leading to notable interactions and chemical shifts.

• Specific peaks are correlated to functional groups such as carboxylic acids and halides.

Page 2: Chemical Structure and J values

• Splitting patterns: Further breakdown of J values and relationships between protons.

• C=C Structure: Notable how J values correspond to cis and trans arrangements.

• Discusses geminal and trans configurations influencing peak shapes in the spectrum.

Page 3: 13C NMR Analysis

• 13C NMR: Distinguishes carbon types and recognizes that only carbon can generate signals (C) in NMR.

• Carbon Peaks: Importance of single peaks and no coupling in carbon NMR.

• Techniques: DEPT (Distortionless Enhancement by Polarization Transfer) reveals attached hydrogens:

  • DEPT90 shows only CH carbons.

  • DEPT135 differentiates between positive and negative signals for CH3 and CH2.

Page 4: Proton Analysis and Aromaticity

• Hydrogen Protons: Singlets observed in certain configurations and their implications.

• Discusses aromatic protons and coupling with nearby atoms.

• Chemical shifts for various environments including deshielding effects in nitrobenzene and anisole structures.

Page 5: Conjugated Systems and Stability

• Conjugation: Describes the characteristics and stability of conjugated systems versus isolated dienes.

• Energy considerations: Stability is related to bond formations, highlighting Diels-Alder reactions.

• Observing heat of hydrogenation as an indicator of stability in reaction mechanisms.

Page 6: Diels-Alder Reaction Specifics

• Reaction Conditions: Discusses the required structure of dienes for Diels-Alder, especially S-cis configuration.

• Dicyclopentadiene and other locked structures detailed in terms of reactivity.

Page 7: Stereospecificity of Diels-Alder Reaction

• Stereospecific nature of Diels-Alder observed; Cis structures remain cis while trans structures yield different configurations.

• Focus on regioselective reactions and their outcomes under various substituents.

Page 8: Electrophilic Addition to Dienes

• Mechanisms of electrophilic addition and temperature's influence on addition products.

• Kinetic vs Thermodynamic Control: Low temperatures favor 1,2-addition, while high temperatures favor 1,4-addition.

Page 9: UV Spectroscopy and Conjugation

• UV Absorption: Discusses wavelength range of UV light and its relevance in obtaining energy from bonding.

• Effects of conjugation on color properties in natural pigments, detailing relationship between structure and absorbed wavelengths.

Page 10: Aromatic Compounds and Benzene

• Aromaticity: Definition and criteria, including Huckel’s rule.

• Delocalization: Flat planar structures require specific orbital arrangements for resonance.

Page 11: Basicity and Aromaticity

• Discusses lone pair involvement in aromatic vs non-aromatic compounds.

• Basicity trends for substituted benzenes and implications of hybridization on aromatic properties.

Page 12: Priority in Substitution Nomenclature

• Nomenclature rules for aromatic compounds and priorities in substituents to yield minimum numbering on phenol derivatives.

• Evaluates various functional groups to determine correct nomenclature for substituted aromatic compounds.

Page 13: Electrophilic Aromatic Substitution (EAS)

• Mechanisms of electrophilic substitutions on benzene, highlighting catalysts like FeBr3.

• Reaction condition details indicating the stability of intermediates involved in Br + HBr reactions.

Page 14: Nitration Reaction Specifics

• Nitration of Benzene: Describes procedures and considerations for adding nitro groups in aromatic compounds,

  • Importance of Lewis acidity in the process.